1. Processing method and processing accuracy of outer circular surface
Shaft, sleeve, and disc parts are typical parts with an outer circular surface. The commonly used machining methods for the outer circular surface are turning, grinding and various finishing methods. Turning is the most cost-effective processing method for the outer circular surface, but in terms of its economic accuracy, it is generally suitable as a rough machining and semi-finishing method for the outer circular surface; Grinding processing is the main finishing method of the outer circular surface, especially suitable for finishing parts after various high hardness and quenching; Photofinishing is an ultra-precision machining method (such as rolling, polishing, grinding, etc.) after finishing, which is suitable for certain parts with high precision and surface quality requirements. Since the economic machining accuracy, surface roughness, productivity and production cost that can be achieved by various processing methods are different, it is necessary to select a reasonable processing method according to the specific situation, so as to process qualified parts that meet the requirements on the part drawings.
2. Turning processing of outer circular surface
(1) The main processing method of the outer circular surface of the shaft parts in the form of external turning is turning processing. The main processing forms are: waste car free forgings and large castings of blanks, processing allowance is very large, in order to reduce the blank outer circle shape error and position deviation, so that the subsequent process processing allowance is uniform, to remove the outer surface of the oxide scale based on the outer circle processing, the general cutting margin is 1-3mm on one side. Rough turning Small and medium-sized forging and casting blanks are generally directly rough turned. Rough turning mainly cuts most of the margin of the blank (generally out of the step profile), and when the rigidity of the process system allows, a larger cutting amount should be selected to improve production efficiency. Semi-finishing turns are generally used as a final machining process for medium-precision surfaces, but can also be used as a pre-machining process for grinding and other machining operations. For blanks with high precision, it can be directly semi-finished without rough turning. Finishing turning Final machining process for outer circular surface processing and pre-processing before finishing machining. Fine Vehicle Final processing process for high-precision, fine-roughness surfaces. It is suitable for the outer circular surface processing of non-ferrous metal parts, but because non-ferrous metals are not suitable for grinding, fine turning can be used instead of grinding processing. However, fine turning requires machine tools with high precision, good rigidity, stable transmission, micro feed, and no crawling phenomenon. Diamond or carbide tools are used in turning, the main declination angle of the tool is larger (45 o -90 o), and the arc radius of the tool tip is less than 0.1-1.0mm, [1]
(2) Application of turning methods
1) Ordinary turning is suitable for various batches of shaft parts external circular processing, and is widely used. Single small batches often use bedroom lathes to complete turning processing; Medium batch and mass production use automatic, semi-automatic lathes and special lathes to complete turning processing. 2) CNC turning is suitable for single-piece small batch and medium batch production. The application is becoming more and more common, and its main advantages are good flexibility, short equipment adjustment and preparation time when replacing machined parts; Less auxiliary time during machining, which can improve efficiency by optimizing cutting parameters and adapting control; Good processing quality, less special fixtures, low corresponding production preparation cost; The technical requirements of machine tool operation are low, and it is not affected by the skills, vision, spirit, physical strength and other factors of the operator. For shaft parts, CNC turning is suitable for the following characteristics. Parts with complex structure or shape, difficult ordinary processing operations, long man-hours and low processing efficiency. Parts with high requirements for consistency in machining accuracy. Parts with variable cutting conditions, such as parts that need to be grooved, turned, turned threads, etc. due to shape characteristics, should change the cutting amount many times during processing. The batch is not large, but each batch of parts with variable varieties and a certain degree of complexity pair with keyway, radial hole (including screw hole), end face with distributed hole (including screw hole) system of shaft parts, such as shaft with flange, shaft with keyway or square head, can also be processed on the turning machining center, in addition to ordinary CNC turning, various grooves, holes (including screw holes), surfaces and other processing surfaces on the parts can also be processed. The process is highly concentrated, its processing efficiency is higher than ordinary CNC turning, and the machining accuracy is more stable and reliable. 3) The method of processing the workpiece surface with an abrasive tool for grinding the outer surface at a high linear speed is called grinding. Grinding is a high-speed cutting method with multiple tools and edges, which is used for part finishing and hard surface machining. Grinding has a wide range of processes and can be divided into coarse grinding, fine grinding, fine grinding and mirror grinding. The abrasives (or abrasives) used in grinding processing have the characteristics of small particles, high hardness and good heat resistance, so hard metal materials and non-metallic materials can be processed, such as hardened steel, carbide tools, ceramics, etc.; In the process of machining, there are many particles participating in the cutting movement at the same time, and extremely thin and very fine chips can be removed, so the machining accuracy is high and the surface roughness value is small. As a finishing method, grinding is widely used in production. Thanks to the development of intensive grinding, the stock can also be ground directly to the required dimensions and precision, resulting in high productivity.
